This invention relates to the field of earth formation testing and, more particularly to a method for determining the virgin temperature of formations surrounding an earth borehole.
The undisturbed (or virgin) formation temperature at depth regions of interest is usually estimated from open hole and cased hole logging tools measurements, and from slick line temperature and pressure gauges. These are actually wellbore fluid measurements. The stabilized temperature from sampling/pump-out measurements from formation testing tools has also been used to obtain formation temperature.
There is a need for a rigorous technique to obtain actual formation temperature using, for example, measurements from a formation testing tool. Production data has shown that actual fluid temperatures arriving at production facilities are significantly higher than those calculated based on early formation pressure estimations. Accurate temperature prediction has great impact on the effectiveness of the following: flow assurance designs including paraffin and asphaltene deposition, and hydrate formation; production casing and tubing design, including expensive tubing insulation design; and production facility design. In high cost fields, such as deepwater and ultra-deep wells, temperature impacts wellbore construction, and sub-sea and surface production facilities that can be extremely expensive.
Some representative prior art approaches for temperature determination will next be listed. The approach of S. V. Kashikar and F. C. Arnold, “Determination of Formation Temperature From Flow Tests: A New Solution”, SPE 21707, Production Operations Symposium, Oklahoma City, Okla., Apr. 7-9, 1991, includes determination of formation temperature from flow tests. The approach of L. R. Raymond, “Temperature Distribution in a Circulating Drilling Fluid”, SPE 2320, JPT, March, 1969, includes determination of temperature distribution in a circulating drilling fluid. The approach of M. N. Hashem (2002): “Measuring The In Situ Static Formation Temperature”, Published PCT International Patent Application WO 02/057595 A1, 25 Jul. 2002, includes measuring the temperature of fluid produced by a wireline tool when the formation fluid is substantially uncontaminated. Reference can also be made to U.S. Pat. Nos. 4,575,261 and 5,159,569.